Ground-level ozone
pollution, also known as
smog, is eating away at
agriculture all over the
world. Worse yet, new
research in Europe
reveals the damage to
crops isn't always visible.

Crop yields of winter
oilseed rape, a common
crop in the UK, fell by as
much as 14 percent when
plots were exposed to
high levels of ozone.
Similar field trials on winter wheat, another major UK crop, produced a 13
percent loss in yields.

Previous research based solely on laboratory experiments indicated crop
yields were unlikely to be affected by ozone because plants in the study
showed no visible signs of foliage damage.

"Effects on productivity occurred in the absence of visible leaf injury, so
would not have been noticed without a controlled experiment," said Tom
Lyons, a researcher in the air pollution lab in the Department of Agricultural
and Environmental Science at the University of Newcastle upon Tyne, where
some of the research was conducted. "For rape, the quality of the seed was
detrimentally affected by ozone, again inferring the pollutant may be having
'invisible' effects on agricultural production."

Ground-level ozone is created when nitrogen oxide emissions, primarily from
automobiles and power plants, react with oxygen in the air. Although
controls exist in the UK for emissions of ozone precursor gases such as
nitrogen oxide from vehicles and industrial plants, pollutants still manage to
travel far and wide, damaging crops and impacting human health in rural
areas.

Ground-level ozone interferes with a plant's ability to produce and store
food, so that growth, reproduction and overall health are compromised.
Plants exposed to ozone are more susceptible to disease, pests and
environmental stresses.

In the United States, smog has been shown to reduce agricultural yields for
vital crops such as soybeans, kidney beans, wheat and cotton.

There are options to help lessen ozone's insidious effects, according to
Lyons. They include resistant crop varieties, chemicals specially developed
to protect crops from ozone, conventional breeding programs and transgenic
technology to develop more ozone resistant plants.

In the study, crops grown
in field plots on
University of Newcastle
land were exposed to
controlled doses of
ozone. While there was
no visible damage to the
crops, researcher John
Ollerenshaw found that in
oilseed rape, for
example, the number of
flowering branches
produced by individual
plants fell by 38 percent.
The plants compensated
in part by producing
more and larger seeds
per pod.

Nevertheless, in the most
sensitive variety of
oilseed rape, Eurol, seed
yield fell by 14 percent, a
loss equivalent to $26.31
per ton. The oil content
of the seeds fell by 5 percent, a loss equivalent to another $13.07 per ton.

In winter wheat, the number of grains per ear declined while the number of
infertile florets increased, resulting in a 13 percent yield reduction.

Research was also conducted on crops in Spain and other Mediterranean
countries where crop damage is more severe than in the UK. Crop damage
is visible in some areas of these countries; older leaves become discolored
and eventually die.

In eastern Spain, watermelons grown in open-top chambers showed a 19
percent drop in yields. In this study, ozone levels were double the guidelines
set by the United Nations Economic Commission for Europe. In the second
year of the study, ozone levels were five times the guideline, resulting in a 39
percent loss in yields.

The findings will help UK officials review and possibly revise their policy on
atmospheric pollution. Based on their research, the scientists have also
advised the United Nations to re-examine its intervention policies.

"These findings draw attention to the need for exposure-response
relationships to be examined in a wider range of crops grown over a broader
range of climatic conditions, particularly those prevalent in the Mediterranean
region," said Barnes. "Until the results of such studies are available, critical
levels aimed at the protection of crop yield in Europe will remain valid only
for a defined range of climatic conditions."

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